EMB145 Captain experiences failure of both primary and backup trim channels shortly after takeoff. QRH procedures do not resolve the problem and crew elects to return to departure airport. The same problem had occurred previously according to the maintenance log.

Narrative

On climbout we experienced a failure of both trim channels; first the primary followed within a second or two by the back-up. The pilot flying hit the quick disconnect and held the button; while I ran through the QRH procedures. We were unable to re-engage either trim channel per the procedure in the QRH and elected to return as a precaution. I notified Maintenance Control and Operations; told ATC that we were declaring an emergency and returning. I wanted CFR near by in case of a possible brake over temp/fire or any other unforeseen scenarios. I calculated the landing distance for both nose down and nose up tendencies; and found that at our heavy weight we would have enough performance to safely land on any of the 3 runways. We continued to fly to the northwest of the airport to burn off a little more fuel and lighten the aircraft as well as lose altitude. I briefed the approach at this time and took the flight controls for the landing. Landing was uneventful; and we taxied back to the terminal and parked under the protection of CFR. Deplaning was uneventful; all passengers disembarked calmly up the jetway.This aircraft had the same thing happen the previous day according to the maintenance log; and was checked and signed off by Maintenance. This was little more than an aircraft system failure; the cause of the failure is unknown.