Powerful converter 12 24V mc34063. Pulse converter on MC34063A

Very often the question arises of how to obtain the voltage required for a power supply circuit, having a source with a different voltage from the required one. Such tasks are divided into two: when: you need to reduce or increase the voltage to a given value. This article will consider the first option.

As a rule, you can use a linear stabilizer, but it will have large power losses, because it will convert the difference in voltage into heat. This is where pulse converters come to the rescue. We present to your attention a simple and compact converter based on the MC34063.

This chip is very versatile, it can implement buck, boost and inverting converters with a maximum internal current of up to 1.5A. But this article only discusses the step-down converter, the rest will be discussed later.

The dimensions of the resulting converter are 21x17x11 mm. Such dimensions were obtained due to the use of lead and SMD parts together. The converter contains only 9 parts.

The parts in the circuit are designed for 5V with a current limit of 500mA, with a ripple of 43kHz and 3mV. The input voltage can be from 7 to 40 volts.

The resistor divider on R2 and R3 is responsible for the output voltage; if you replace them with a trimming resistor of about 10 kOhm, then you can set the required output voltage. Resistor R1 is responsible for limiting the current. Capacitor C1 and coil L1 are responsible for the ripple frequency, and capacitor C3 is responsible for the ripple level. The diode can be replaced with 1N5818 or 1N5820. To calculate the circuit parameters there is a special calculator - http://www.nomad.ee/micros/mc34063a/index.shtml, where you just need to set the required parameters, it can also calculate the circuits and parameters of the two types of converters not considered.

2 printed circuit boards were made: on the left - with a voltage divider on a voltage divider made of two resistors of standard size 0805, on the right - with a variable resistor 3329H-682 6.8 kOhm. The MC34063 microcircuit is in a DIP package, under it are two chip tantalum capacitors of standard size - D. Capacitor C1 is of standard size 0805, an output diode, a current limiting resistor R1 - half a watt, at low currents, less than 400 mA, you can install a resistor of lower power. Inductance CW68 22uH, 960mA.

Ripple waveforms, R limit = 0.3 Ohm

These oscillograms show ripples: on the left - without a load, on the right - with a load in the form of a cell phone, limiting a 0.3 Ohm resistor, below with the same load, but limiting a 0.2 Ohm resistor.

Ripple waveform, R limit = 0.2 Ohm

The characteristics taken (not all parameters were measured), with an input voltage of 8.2 V.

This adapter was made to recharge a cell phone and power digital circuits while traveling.

The article showed a board with a variable resistor as a voltage divider, I will add the corresponding circuit to it, the difference from the first circuit is only in the divider.

This opus will be about 3 heroes. Why heroes?))) Since ancient times, heroes are the defenders of the Motherland, people who “stole”, that is, saved, and not, as now, “stole”, wealth.. Our drives are pulse converters, 3 types (step-down, step-up, inverter ). Moreover, all three are on one MC34063 chip and on one type of DO5022 coil with an inductance of 150 μH. They are used as part of a microwave signal switch using pin diodes, the circuit and board of which are given at the end of this article.

Calculation of a DC-DC step-down converter (step-down, buck) on the MC34063 chip

The calculation is carried out using the standard “AN920/D” method from ON Semiconductor. The electrical circuit diagram of the converter is shown in Figure 1. The numbers of the circuit elements correspond to the latest version of the circuit (from the file “Driver of MC34063 3in1 – ver 08.SCH”).

Fig. 1 Electrical circuit diagram of a step-down driver.

IC outputs:

Conclusion 1 - SWC(switch collector) - output transistor collector

Conclusion 2 - S.W.E.(switch emitter) - emitter of the output transistor

Conclusion 3 - TS(timing capacitor) - input for connecting a timing capacitor

Conclusion 4 - GND– ground (connects to the common wire of the step-down DC-DC)

Conclusion 5 - CII(FB) (comparator inverting input) - inverting input of the comparator

Conclusion 6 - VCC- nutrition

Conclusion 7 - Ipk— input of the maximum current limiting circuit

Conclusion 8 - DRC(driver collector) - collector of the output transistor driver (a bipolar transistor connected according to a Darlington circuit, located inside the microcircuit, is also used as an output transistor driver).

Elements:

L 3— throttle. It is better to use an open type inductor (not completely closed with ferrite) - DO5022T series from Oilkraft or RLB from Bourns, since such an inductor enters saturation at a higher current than the common closed type CDRH Sumida inductors. It is better to use chokes with higher inductance than the calculated value obtained.

From 11- timing capacitor, it determines the conversion frequency. The maximum conversion frequency for 34063 chips is about 100 kHz.

R 24, R 21— voltage divider for the comparator circuit. The non-inverting input of the comparator is supplied with a voltage of 1.25V from the internal regulator, and the inverting input is supplied from a voltage divider. When the voltage from the divider becomes equal to the voltage from the internal regulator, the comparator switches the output transistor.

C 2, C 5, C 8 and C 17, C 18— output and input filters, respectively. The output filter capacitance determines the amount of output voltage ripple. If during the calculations it turns out that a very large capacitance is required for a given ripple value, you can do the calculation for large ripples, and then use an additional LC filter. The input capacitance is usually taken 100 ... 470 μF (TI recommendation is at least 470 μF), the output capacitance is also taken 100 ... 470 μF (taken 220 μF).

R 11-12-13 (Rsc)- current-sensing resistor. It is needed for the current limiting circuit. Maximum output transistor current for MC34063 = 1.5A, for AP34063 = 1.6A. If the peak switching current exceeds these values, the microcircuit may burn out. If it is known for sure that the peak current does not even come close to the maximum values, then this resistor can not be installed. The calculation is carried out specifically for the peak current (of the internal transistor). When using an external transistor, the peak current flows through it, while a smaller (control) current flows through the internal transistor.

VT 4 an external bipolar transistor is placed in the circuit when the calculated peak current exceeds 1.5A (at a large output current). Otherwise, overheating of the microcircuit can lead to its failure. Operating mode (transistor base current) R 26 , R 28 .

VD 2 – Schottky diode or ultrafast diode for voltage (forward and reverse) of at least 2U output

Calculation procedure:

  • Select rated input and output voltages: V in, Vout and maximum

output current I out.

In our scheme V in =24V, V out =5V, I out =500mA(maximum 750 mA)

  • Select the minimum input voltage V in(min) and minimum operating frequency fmin with selected V in And I out.

In our scheme V in(min) =20V (according to technical specifications), choose f min =50 kHz

3) Calculate the value (t on +t off) max according to the formula (t on +t off) max =1/f min, t on(max)— maximum time when the output transistor is open, toff(max)— maximum time when the output transistor is closed.

(t on +t off) max =1/f min =1/50kHz=0.02 MS=20 μS

Calculate ratio t on/t off according to the formula t on /t off =(V out +V F)/(V in(min) -V sat -V out), Where V F- voltage drop across the diode (forward - forward voltage drop), V sat- the voltage drop across the output transistor when it is in a fully open state (saturation - saturation voltage) at a given current. V sat determined from the graphs or tables given in the documentation. From the formula it is clear that the more V in, Vout and the more they differ from each other, the less influence they have on the final result V F And V sat.

(t on /t off) max =(V out +V F)/(V in(min) -V sat -V out)=(5+0.8)/(20-0.8-5)=5.8/14.2=0.408

4) Knowing t on/t off And (t on +t off) max solve the system of equations and find t on(max).

t off = (t on +t off) max / ((t on /t off) max +1) =20μS/(0.408+1)=14.2 μS

t on (max) =20- t off=20-14.2 µS=5.8 µS

5) Find the capacitance of the timing capacitor From 11 (Ct) according to the formula:

C 11 = 4.5*10 -5 *t on(max).

C 11 = 4.5*10 -5 * t on (max) =4.5*10 - 5*5.8 µS=261pF(this is the min value), take 680pF

The smaller the capacitance, the higher the frequency. Capacitance 680pF corresponds to frequency 14KHz

6) Find the peak current through the output transistor: I PK(switch) =2*I out. If it turns out to be greater than the maximum current of the output transistor (1.5 ... 1.6 A), then a converter with such parameters is impossible. It is necessary to either recalculate the circuit for a lower output current ( I out), or use a circuit with an external transistor.

I PK(switch) =2*I out =2*0.5=1A(for maximum output current 750mA I PK(switch) = 1.4A)

7) Calculate Rsc according to the formula: R sc =0.3/I PK(switch).

R sc =0.3/I PK(switch) =0.3/1=0.3 Ohm, We connect 3 resistors in parallel ( R 11-12-13) 1 ohm

8) Calculate the minimum capacitance of the output filter capacitor: C 17 =I PK(switch) *(t on +t off) max /8V ripple(p-p), Where V ripple(p-p)— maximum value of output voltage ripple. The maximum capacity is taken from the standard values ​​closest to the calculated one.

From 17 =I PK (switch) *(t on+ t off) max/8 V ripple (pp) =1*14.2 µS/8*50 mV=50 µF, take 220 µF

9) Calculate the minimum inductance of the inductor:

L 1(min) = t on (max) *(V in (min) V satVout)/ I PK (switch) . If C 17 and L 1 are too large, you can try to increase the conversion frequency and repeat the calculation. The higher the conversion frequency, the lower the minimum capacitance of the output capacitor and the minimum inductance of the inductor.

L 1(min) =t on(max) *(V in(min) -V sat -V out)/I PK(switch) =5.8μS *(20-0.8-5)/1=82.3 µH

This is the minimum inductance. For the MC34063 microcircuit, the inductor should be selected with a deliberately larger inductance value than the calculated value. We choose L=150μH from CoilKraft DO5022.

10) Divider resistances are calculated from the ratio V out =1.25*(1+R 24 /R 21). These resistors must be at least 30 ohms.

For V out = 5V we take R 24 = 3.6K, thenR 21 =1.2K

Online calculation http://uiut.org/master/mc34063/ shows the correctness of the calculated values ​​(except Ct=C11):

There is also another online calculation http://radiohlam.ru/teory/stepdown34063.htm, which also shows the correctness of the calculated values.

12) According to the calculation conditions in paragraph 7, the peak current of 1A (Max 1.4A) is near the maximum current of the transistor (1.5 ... 1.6 A). It is advisable to install an external transistor already at a peak current of 1A, in order to avoid overheating of the microcircuit. This is done. We select transistor VT4 MJD45 (PNP type) with a current transfer coefficient of 40 (it is advisable to take h21e as high as possible, since the transistor operates in saturation mode and the voltage drops across it is about = 0.8V). Some transistor manufacturers indicate in the datasheet title that the saturation voltage Usat is low, about 1V, which is what you should be guided by.

Let's calculate the resistance of resistors R26 and R28 in the circuits of the selected transistor VT4.

Base current of transistor VT4: I b= I PK (switch) / h 21 uh . I b=1/40=25mA

Resistor in the BE circuit: R 26 =10*h21e/ I PK (switch) . R 26 =10*40/1=400 Ohm (take R 26 =160 Ohm)

Current through resistor R 26: I RBE =V BE /R 26 =0.8/160=5mA

Resistor in the base circuit: R 28 =(Vin(min)-Vsat(driver)-V RSC -V BEQ 1)/(I B +I RBE)

R 28 =(20-0.8-0.1-0.8)/(25+5)=610 Ohms, you can take less than 160 Ohms (same type as R 26, since the built-in Darlington transistor can provide more current for a smaller resistor.

13) Calculate the snubber elements R 32, C 16. (see the calculation of the boost circuit and the diagram below).

14) Let's calculate the elements of the output filter L 5 , R 37, C 24 (G. Ott “Methods for suppressing noise and interference in electronic systems” p. 120-121).

I chose - coil L5 = 150 µH (same type choke with active resistive resistance Rdross = 0.25 ohm) and C24 = 47 µF (the circuit indicates a larger value of 100 µF)

Let's calculate the filter attenuation decrement xi =((R+Rdross)/2)* root(C/L)

R=R37 is set when the attenuation decrement is less than 0.6, in order to remove the overshoot of the relative frequency response of the filter (filter resonance). Otherwise, the filter at this cutoff frequency will amplify the oscillations rather than attenuate them.

Without R37: Ksi=0.25/2*(root 47/150)=0.07 - the frequency response will rise to +20dB, which is bad, so we set R=R37=2.2 Ohm, then:

C R37: Xi = (1+2.2)/2*(root 47/150) = 0.646 - with Xi 0.5 or more, the frequency response decreases (there is no resonance).

The resonant frequency of the filter (cutoff frequency) Fср=1/(2*pi*L*C) must lie below the conversion frequencies of the microcircuit (thus filtering these high frequencies 10-100 kHz). For the indicated values ​​of L and C, we obtain Faver = 1896 Hz, which is less than the operating frequency of the converter 10-100 kHz. Resistance R37 cannot be increased by more than a few Ohms, as the voltage across it will drop (with a load current of 500mA and R37=2.2 Ohms, the voltage drop will be Ur37=I*R=0.5*2.2=1.1V).

All circuit elements are selected for surface mounting

Oscillograms of operation at various points in the buck converter circuit:

15) a) Oscillograms without load ( Uin=24V, Uout=+5V):

Voltage +5V at the output of the converter (on capacitor C18) without load

The signal at the collector of transistor VT4 has a frequency of 30-40Hz, since without load,

the circuit consumes about 4 mA without load

Control signals on pin 1 of the microcircuit (lower) and

based on transistor VT4 (upper) without load

b) Oscillograms under load(Uin=24V, Uout=+5V), with frequency-setting capacitance c11=680pF. We change the load by decreasing the resistance of the resistor (3 oscillograms below). The output current of the stabilizer increases, as does the input.

Load - 3 68 ohm resistors in parallel ( 221 mA)

Input current – ​​70mA

Yellow beam - transistor-based signal (control)

Blue beam - signal at the collector of the transistor (output)

Load - 5 68 ohm resistors in parallel ( 367 mA)

Input current – ​​110mA

Yellow beam - transistor-based signal (control)

Blue beam - signal at the collector of the transistor (output)

Load - 1 resistor 10 ohm ( 500 mA)

Input current – ​​150mA

Conclusion: depending on the load, the pulse repetition frequency changes, with a higher load the frequency increases, then the pauses (+5V) between the accumulation and release phases disappear, only rectangular pulses remain - the stabilizer works “at the limit” of its capabilities. This can also be seen in the oscillogram below, when the “saw” voltage has surges - the stabilizer enters current limiting mode.

c) Voltage at the frequency-setting capacitance c11=680pF at a maximum load of 500mA

Yellow beam - capacitance signal (control saw)

Blue beam - signal at the collector of the transistor (output)

Load - 1 resistor 10 ohm ( 500 mA)

Input current – ​​150mA

d) Voltage ripple at the output of the stabilizer (c18) at a maximum load of 500 mA

Yellow beam - pulsation signal at the output (s18)

Load - 1 resistor 10 ohm ( 500 mA)

Voltage ripple at the output of the LC(R) filter (c24) at a maximum load of 500 mA

Yellow beam - ripple signal at the output of the LC(R) filter (c24)

Load - 1 resistor 10 ohm ( 500 mA)

Conclusion: the peak-to-peak ripple voltage range decreased from 300mV to 150mV.

e) Oscillogram of damped oscillations without a snubber:

Blue beam - on a diode without a snubber (insertion of a pulse over time is visible

not equal to the period, since this is not PWM, but PFM)

Oscillogram of damped oscillations without snubber (enlarged):

Calculation of a step-up, boost DC-DC converter on the MC34063 chip

http://uiut.org/master/mc34063/. For the boost driver, it is basically the same as the buck driver calculation, so it can be trusted. During online calculation, the scheme automatically changes to the standard scheme from “AN920/D”. Input data, calculation results and the standard scheme itself are presented below.

— field-effect N-channel transistor VT7 IRFR220N. Increases the load capacity of the microcircuit and allows for quick switching. Selected by: The electrical circuit of the boost converter is shown in Figure 2. The numbers of circuit elements correspond to the latest version of the circuit (from the file “Driver of MC34063 3in1 – ver 08.SCH”). The scheme contains elements that are not included in the standard online calculation scheme. These are the following elements:

  • Maximum drain-source voltage V DSS =200V, because the output voltage is high +94V
  • Low channel voltage drop RDS(on)max =0.6Om. The lower the channel resistance, the lower the heating losses and the higher the efficiency.
  • Small capacitance (input), which determines the gate charge Qg (Total Gate Charge) and low input gate current. For a given transistor I=Qg*FSW=15nC*50 KHz=750uA.
  • Maximum drain current Id=5A, since pulse current Ipk=812 mA at output current 100 mA

- voltage divider elements R30, R31 and R33 (reduces the voltage for the VT7 gate, which should be no more than V GS = 20V)

- discharge elements of the input capacitance VT7 - R34, VD3, VT6 when switching the transistor VT7 to the closed state. Reduces the decay time of the VT7 gate from 400nS (not shown) to 50nS (waveform with a decay time of 50nS). Log 0 on pin 2 of the microcircuit opens the PNP transistor VT6 and the input gate capacitance is discharged through the CE junction VT6 (faster than simply through resistor R33, R34).

— the coil L turns out to be very large when calculating, a lower nominal value L = L4 (Fig. 2) = 150 μH is selected

— snubber elements C21, R36.

Snubber calculation:

Hence L=1/(4*3.14^2*(1.2*10^6)^2*26*10^-12)=6.772*10^4 Rsn=√(6.772*10^4 /26*10^- 12)=5.1KOhm

The size of the snubber capacitance is usually a compromise solution, since, on the one hand, the larger the capacitance, the better the smoothing (less number of oscillations), on the other hand, each cycle the capacitance is recharged and dissipates part of the useful energy through the resistor, which affects the efficiency (usually A normally designed snubber reduces efficiency very slightly, within a couple of percent).

By installing a variable resistor, we determined the resistance more accurately R=1 K

Fig.2 Electrical circuit diagram of a step-up, boost driver.

Oscillograms of operation at various points in the boost converter circuit:

a) Voltage at various points without load:

Output voltage - 94V without load

Gate voltage without load

Drain voltage without load

b) voltage at the gate (yellow beam) and at the drain (blue beam) of transistor VT7:

on the gate and drain under load the frequency changes from 11 kHz (90 µs) to 20 kHz (50 µs) - this is not PWM, but PFM

on the gate and drain under load without a snubber (stretched - 1 oscillation period)

on gate and drain under load with snubber

c) leading and trailing edge voltage pin 2 (yellow beam) and on the gate (blue beam) VT7, saw pin 3:

blue - 450 ns rise time on VT7 gate

Yellow - rise time 50 ns per pin 2 chips

blue - 50 ns rise time on VT7 gate

saw on Ct (pin 3 of IC) with control release F=11k

Calculation of DC-DC inverter (step-up/step-down, inverter) on the MC34063 chip

The calculation is also carried out using the standard “AN920/D” method from ON Semiconductor.

The calculation can be done immediately “online” http://uiut.org/master/mc34063/. For an inverting driver, it is basically the same as the calculation for a buck driver, so it can be trusted. During online calculation, the scheme automatically changes to the standard scheme from “AN920/D”. Input data, calculation results and the standard scheme itself are presented below.

— bipolar PNP transistor VT7 (increases load capacity) The electrical circuit of the inverting converter is shown in Figure 3. The numbers of circuit elements correspond to the latest version of the circuit (from the file “Driver of MC34063 3in1 – ver 08.SCH”). The scheme contains elements that are not included in the standard online calculation scheme. These are the following elements:

— voltage divider elements R27, R29 (sets the base current and operating mode of VT7),

— snubber elements C15, R35 (suppresses unwanted vibrations from the throttle)

Some components differ from those calculated:

  • coil L is taken less than the calculated value L = L2 (Fig. 3) = 150 μH (all coils are of the same type)
  • output capacitance is taken less than the calculated one C0=C19=220uF
  • The frequency-setting capacitor is taken C13=680pF, corresponding to a frequency of 14KHz
  • divider resistors R2=R22=3.6K, R1=R25=1.2K (taken first for output voltage -5V) and final resistors R2=R22=5.1K, R1=R25=1.2K (output voltage -6.5V)

The current limiting resistor is taken Rsc - 3 resistors in parallel, 1 Ohm each (resulting resistance 0.3 Ohm)

Fig.3 Electrical circuit diagram of the inverter (step-up/step-down, inverter).

Oscillograms of operation at various points of the inverter circuit:

a) with input voltage +24V without load:

output -6.5V without load

on the collector – accumulation and release of energy without load

on pin 1 and the base of the transistor without load

on the base and collector of the transistor without load

output ripple without load

Let's consider a typical circuit of a boost DC/DC converter based on 34063 chips:

IC outputs:

  1. SWC(switch collector) - output transistor collector
  2. S.W.E.(switch emitter) - emitter of the output transistor
  3. Tc(timing capacitor) - input for connecting a timing capacitor
  4. GND- Earth
  5. CII(comparator inverting input) - inverting input of the comparator
  6. Vcc- nutrition
  7. Ipk— input of the maximum current limiting circuit
  8. DRC(driver collector) - output transistor driver collector (a bipolar transistor is also used as an output transistor driver)

Elements:

L 1— storage choke. This is, in general, an element of energy conversion.

C 1- timing capacitor, it determines the conversion frequency. The maximum conversion frequency for 34063 chips is about 100 kHz.

R2, R1— voltage divider for the comparator circuit. The non-inverting input of the comparator is supplied with a voltage of 1.25 V from the internal regulator, and the inverting input is supplied from a voltage divider. When the voltage from the divider becomes equal to the voltage from the internal regulator, the comparator switches the output transistor.

C 2, C 3— output and input filters, respectively. The output filter capacitance determines the amount of output voltage ripple. If during the calculations it turns out that a very large capacitance is required for a given ripple value, you can make the calculation for larger ripples, and then use an additional LC filter. Capacitance C 3 is usually taken at 100 ... 470 μF.

Rsc- current-sensing resistor. It is needed for the current limiting circuit. Maximum output transistor current for MC34063 = 1.5A, for AP34063 = 1.6A. If the peak switching current exceeds these values, the microcircuit may burn out. If it is known for sure that the peak current does not even come close to the maximum values, then this resistor can not be installed.

R 3- a resistor that limits the current of the output transistor driver (maximum 100 mA). Usually 180, 200 Ohms are taken.

Calculation procedure:

  1. Select rated input and output voltages: V in, Vout and maximum output current I out.
  2. 2) Select the minimum input voltage V in(min) and minimum operating frequency fmin with selected V in And I out.
  3. Calculate the value (t on +t off) max according to the formula (t on +t off) max =1/f min, t on(max)— maximum time when the output transistor is open, toff(max)— maximum time when the output transistor is closed.
  4. Calculate ratio t on/t off according to the formula t on /t off =(V out +V F -V in(min))/(V in(min) -V sat), Where V F— voltage drop across the output filter, V sat- voltage drop across the output transistor (when it is in the fully open state) at a given current. V sat determined from the graphs given in the documentation for the microcircuit (or for the transistor, if the circuit has an external transistor). From the formula it is clear that the more V in, Vout and the more they differ from each other, the less influence they have on the final result V F And V sat, so if you don’t need super-accurate calculations, then I would advise, already with V in(min)=6-7 V, feel free to take it V F=0, V sat= 1.2 V (regular, mediocre bipolar transistor) and don’t bother.
  5. Knowing t on/t off And (t on +t off) max solve the system of equations and find t on(max).
  6. Find the capacitance of the timing capacitor C 1 according to the formula: C 1 = 4.5*10 -5 *t on(max).
  7. Find the peak current through the output transistor: I PK(switch) =2*I out *(1+t on /t off). If it turns out to be greater than the maximum current of the output transistor (1.5 ... 1.6 A), then a converter with such parameters is impossible. It is necessary to either recalculate the circuit for a lower output current ( I out), or use a circuit with an external transistor.
  8. Calculate Rsc according to the formula: R sc =0.3/I PK(switch).
  9. Calculate the minimum capacitance of the output filter capacitor:
  10. C 2 =I out *t on(max) /V ripple(p-p), Where V ripple(p-p)— maximum value of output voltage ripple. Different manufacturers recommend multiplying the resulting value by a factor from 1 to 9. The maximum capacity is taken from the standard values ​​closest to the calculated value.
  11. Calculate the minimum inductance of the inductor:

    L 1(min) =t on(max) *(V in(min) -V sat)/I PK(switch). If C 2 and L 1 are too large, you can try to increase the conversion frequency and repeat the calculation. The higher the conversion frequency, the lower the minimum capacitance of the output capacitor and the minimum inductance of the inductor.

  12. The divider resistances are calculated from the relation V out =1.25*(1+R 2 /R 1).

Online calculator for calculating the converter:

(for correct calculations, use a dot rather than a comma as the decimal point)

1) Initial data:

(if you do not know the values ​​of V sat , V f , V ripple(p-p), then the calculation will be made for V sat =1.2 V, V f =0 V, V ripple(p-p) =50 mV)

Below is a diagram of a step-up DC-DC converter, built according to the boost topology, which, when a voltage of 5...13V is applied to the input, produces a stable voltage of 19V at the output. Thus, using this converter you can get 19V from any standard voltage: 5V, 9V, 12V. The converter is designed for a maximum output current of about 0.5 A, is small in size and very convenient.

A widely used microcircuit is used to control the converter.

A powerful n-channel MOSFET is used as a power switch, as the most economical solution in terms of efficiency. These transistors have minimal resistance in the open state and, as a result, minimal heating (minimum power dissipation).

Since the 34063 series microcircuits are not suitable for controlling field-effect transistors, it is better to use them in conjunction with special drivers (for example, with a half-bridge upper arm driver) - this will allow you to get steeper edges when opening and closing the power switch. However, in the absence of driver chips, you can use a “poor man’s alternative” instead: a bipolar PNP transistor with a diode and a resistor (in this case it is possible, since the field source is connected to a common wire). When the MOSFET is turned on, the gate is charged through the diode, the bipolar transistor is closed, and when the MOSFET is turned off, the bipolar transistor opens and the gate is discharged through it.

Scheme:

Details:

L1, L2 - inductors 35 μH and 1 μH, respectively. Coil L1 can be wound with a thick wire on a ring from the motherboard, just find a ring with a larger diameter, because the native inductances there are only a few microhenries and you may have to wind them in a couple of layers. We take the L2 coil (for the filter) ready from the motherboard.

C1 - input filter, electrolyte 330 uF/25V

C2 - timing capacitor, ceramic 100 pF

C3 - output filter, electrolyte 220 uF/25V

C4, R4 - snubber, nominal 2.7 nF, 10 Ohm, respectively. In many cases, you can do without it altogether. The values ​​of the snubber elements are highly dependent on the specific wiring. The calculation is carried out experimentally, after the board has been manufactured.

C5 - filter for mikruhi power supply, ceramics 0.1 µF

http://site/datasheets/pdf-data/2019328/PHILIPS/2PA733.html


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    The figure shows a diagram of a simple infrared remote control and a receiver whose executive element is a relay. Due to the simplicity of the remote control circuit, the device can only perform two actions: turn on the relay and turn it off by releasing the S1 button, which may be sufficient for certain purposes (garage doors, opening an electromagnetic lock, etc.). Setting up the circuit is very...

  • 05.10.2014

    The circuit is made using a dual op-amp TL072. A pre-amplifier with coefficient is made on A1.1. amplification by a given ratio R2\R3. R1 is the volume control. Op amp A1.2 has an active three-band bridge tone control. Adjustments are made by variable resistors R7R8R9. Coef. transmission of this node 1. Charged preliminary ULF supply can be from ±4V to ±15V Literature...