[AMPS] Bleeder Resistor

[Rich Measures]

>
>Hi, 
>
>I am wondering about 'the' bleeder resistor in a 4kV DC - 1A power
>supply (230V DC input), must of the designs I found are using a 50uF
>capacitor and something like 100k/250W bleeder.

The first consideration is the voltage rating of the bleeder resistor.  
The mfg's voltage rating always takes priority over the power rating.  
For instance, 5kV is 250w diss. in 100k ohms.  However, the maximum V 
rating may be considerably less.    

>Is there any disadvantage to use a 400k instead? 

No.  Bleeder current has virtually no effect on dynamic load reg. in a 
capacitor filter supply.  .The advantage is less heat.    I use 100k-ohms 
(Matsushita 100k-ohm, 3W)  per 500V for capacitor filter anode and screen 
power supplies. .  .    However, for resonant-choke filter supplies, more 
beeder current is needed to prevent the voltage out from rising to the 
peak value during standby.  On the other hand, with electronic bias 
switching, within 10uS of receiving the Tx enable signal from the 
transceiver, the ZSAC current of the amplifier tube typically provides 
0.1A to 0.5A of additional 'bleeder' load current on the supply.  Thus, 
the issue is not exceeding the peak V rating on the filter capacitor 
during standby.  

-  later, Carsten


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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