gmcjetpilot
New Member
I want to switch 60 watts (inductive) both in on-off cycles (flash p=0.666 sec, 50% duty ~
1.5 Hz) and steady. Thanks. I don't want forced air cooling... but want to see what we
can do.
Heatsink calculation:
Tr = Th - Ta = 60 - 25 = 35°C
Ph = Vh * Ih = 14 * 4.3 = 60W
Rth = Tr / Ph = 35 / 60 = 0.58°C/W (that seems low, forced air needed?)
Going from junction and adding all the R's
Rth(j-a) = 0.5 + 1.1** + 0.58 = 2.2 C/W
T(j-a) = Pd x Rth(j-a) = 60W x 2.2 C/W = 132C temp = that is a little hot but OK.
** metal metal paste or mica+paste, special care taken.
Then WHAT KIND OF HEAT SINK WOULD YOU USE?
I was going to do a DIY copper or alumunum (painted black, except at transistor where
it is polished with paste). Rth should be less than 1.0..... I wanted to keep the heatsink
in the case with some holes. I am seeing to get 0.60 CW heatsink I need an external
heatsink, honking big heat sink. Comments? Ideas.
PROBLEM! I need something small and light... Are my calculations way out to lunch?
Is heatsink'ing a MOSFET with 4.3 amps at 14 volt souce, some big deal? I need a
heatsink, but how big.... thanks.
* Ref transistors (not married to them but T0-220 or through hole is perferred).
SPP80P06P
Continuous Current (Tc=110deg) 64 amp
Power dissipation (TC = 25 °C) 340 W
Thermal resistance, junction - case RthJC = 0.4
(max Junction 175 deg)
STB80PF55/STP80PF55
ID Drain current (continuous) at (Tc = 100°C) 57 amp
PTOT Total dissipation at (TC = 25°C) 300 W
Rthj-case Thermal resistance junction-case max 0.5 °C/W
(max Junction 175C)
1.5 Hz) and steady. Thanks. I don't want forced air cooling... but want to see what we
can do.
- 12-14.1 volt DC system
- ASSUME max heatsink Temp 60C.
- Case is a small 3.5" x 2.5" x 1.7" (can make case bigger)
- Assume ambient T=25C, and Tjunc = (as low as possible <= 120C)
- MOSFET (P-channel, because it has to be, please no why N channel)
- 60 watt On-Off (flash) and On steady (would like 100 watt but lets start w/ 60W)
- The MOSFET P's considered for reference (SEE below)
Heatsink calculation:
Tr = Th - Ta = 60 - 25 = 35°C
Ph = Vh * Ih = 14 * 4.3 = 60W
Rth = Tr / Ph = 35 / 60 = 0.58°C/W (that seems low, forced air needed?)
Going from junction and adding all the R's
Rth(j-a) = 0.5 + 1.1** + 0.58 = 2.2 C/W
T(j-a) = Pd x Rth(j-a) = 60W x 2.2 C/W = 132C temp = that is a little hot but OK.
** metal metal paste or mica+paste, special care taken.
Then WHAT KIND OF HEAT SINK WOULD YOU USE?
I was going to do a DIY copper or alumunum (painted black, except at transistor where
it is polished with paste). Rth should be less than 1.0..... I wanted to keep the heatsink
in the case with some holes. I am seeing to get 0.60 CW heatsink I need an external
heatsink, honking big heat sink. Comments? Ideas.
PROBLEM! I need something small and light... Are my calculations way out to lunch?
Is heatsink'ing a MOSFET with 4.3 amps at 14 volt souce, some big deal? I need a
heatsink, but how big.... thanks.
* Ref transistors (not married to them but T0-220 or through hole is perferred).
SPP80P06P
Continuous Current (Tc=110deg) 64 amp
Power dissipation (TC = 25 °C) 340 W
Thermal resistance, junction - case RthJC = 0.4
(max Junction 175 deg)
STB80PF55/STP80PF55
ID Drain current (continuous) at (Tc = 100°C) 57 amp
PTOT Total dissipation at (TC = 25°C) 300 W
Rthj-case Thermal resistance junction-case max 0.5 °C/W
(max Junction 175C)