Electronics > Projects, Designs, and Technical Stuff
minimum load circuit for lab psu
nemail2:
Ok so i have kind of made a decision to go with the matched-pair npn solution.
That DMMT5551-7-F should be able to dissipate those 6-7mA @ 12.288V max output voltage at V_ADJ.
Any objections?
Jay_Diddy_B:
Hi,
We can look at the impact of temperature with this model:
The temperature of Q1 is stepped from 35C to 100C.
I have added the 47 Ohm emitter resistors to reduce the sensitivity.
The downside to the emitter resistors is that the circuit works above 300mV
Regards,
Jay_Diddy_B
xavier60:
With the added Emitter resistors, might cause some residual voltage at the output when CV is set to zero volts. It wouldn't be much.
Mine causes 9mV.
nemail2:
that does look good, doesn't it? 300mV is certainly better than what I'm having now. also more stable. and still cheaper/less parts than the opamp solution.
residual voltage at the output of the PSU itself? because of the drain? or because of the lack of a drain when set to 0mV where the load circuit isn't working?
sorry for the stupid question...
xavier60:
--- Quote from: nemail2 on May 28, 2019, 06:16:45 am ---that does look good, doesn't it? 300mV is certainly better than what I'm having now. also more stable. and still cheaper/less parts than the opamp solution.
residual voltage at the output of the PSU itself? because of the drain? or because of the lack of a drain when set to 0mV where the load circuit isn't working?
sorry for the stupid question...
--- End quote ---
With mine, the small Base bias current causes a small voltage drop across the Emitter resistor while the regulator is off. This small voltage is transferred to the output via the transistor.
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