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I am designing a low profile space grade buck regulator. I have the following constraints

  1. ICs must be space grade
  2. Low component count
  3. Small size

The converter specifications are as follows. Input voltage varying from 15-25V, Required outputs at 3.8V or 5.6V. I came across this converter design from an LM136 datasheet. Could someone explain the functioning of this circuit.enter image description here I can understand that there is the standard buck regulator configuration and a difference amplifier using the npn transistors. The switching functionality eludes me

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  • \$\begingroup\$ Are you planning to launch it into space? \$\endgroup\$ – winny Jul 19 at 6:03
  • \$\begingroup\$ Well, no, not yet. The idea is to develop a small and cheap solution that can be used with other circuits to optimize the overall design \$\endgroup\$ – Stoic_beast Jul 19 at 6:51
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    \$\begingroup\$ And then launch it into space? \$\endgroup\$ – winny Jul 19 at 6:54
  • \$\begingroup\$ LTC linecard for space grade devices: analog.com/media/en/technical-documentation/… \$\endgroup\$ – Peter Smith Jul 19 at 15:09
  • \$\begingroup\$ Thanks peter, didn't know about the RH3083 and RH3845. These devices were previously not qualified. And yes, if the performance is found satisfactory, I'd use it for develpment \$\endgroup\$ – Stoic_beast Jul 20 at 5:42
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It appears to be a hysteretic buck regulator. Please see link for more details. Briefly, the switch turns on if the output voltage is lower than the setpoint, and off once the output voltage rises again.

There will be an output voltage oscillation around the setpoint, so this type of regulator is not suitable for applications sensitive to some ripple. It's a cheap solution, and sounds interesting for your application.

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  • \$\begingroup\$ It is expected that there would be voltage ripple around the set point. This can be reduced with an additional regulator \$\endgroup\$ – Stoic_beast Jul 20 at 5:45
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Take care about efficiency. The darlington PNP (PN2905 and '3 AMP PNP') has a minimum drop of 2*Vbe. You always loose about 1.5..2V at the switch! There area lot of integrated circuits that just require two external MOS-FETs, an inductor, an output capacitor and some resistors for the feedback. These chips offer better efficiency and better parameters and protection in case of overload.

I suggest you check the WEB sites of TI, Linear technology, ST Microelectronics, Maxim ... for data sheets if you need high efficiency solutions. But I have no idea which of these chips are space grade.

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Pretty sure that is a hysteresis mode converter, the long tailed pair shares an emitter resistor making it a schmitt trigger and the 10k resistor just to the right of the switching devices in combination with the 200R resistor from the reference moves the threshold up and down to give the hysteresis.

There is some feed forward via the 39k resistor as well to help input side regulation.

Crude, not going to win any efficiency awards, but all discrete and fairly simple.

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